This invention relates to human respiration in general.
More particularly, the invention relates to a method of supplying the external respiratory organs with breathing air, and to a respiratory apparatus for carrying out this method.
During inhalation a suction or partial vacuum is created in the outer respiratory passages of the human body, and conversely pressure is created in these passages during exhalation. When it is necessary for a human being to wear respiratory apparatus, for example in space, in contaminated atmospheres, in smoke-filled rooms and similar applications, this alternating pressure cycle during breathing is transmitted to the respiratory apparatus being used and is employed to control the functioning of the apparatus. What this amounts to, in effect, is an extension of the natural breathing passages by the respiratory apparatus without, however, interfering in any way with the normal physiology of breathing. This system of artificially supplying air for respiration is thus in keeping with the normal functioning of the human body and would be the optimal solution if the additional resistance offered to breathing by the use of the apparatus (i.e. the pressure fluctuations for inhalation and exhalation) and the increase in the dead air spaces occasioned by the use of the apparatus, could be maintained sufficiently low so as to avoid making breathing too difficult.
This type of breathing equipment presents, however, certain problems which have heretofore not been overcome.
A particular problem is the question how to tightly connect the breathing apparatus to the external respiratory organs of the user. All such equipment utilizes a mask of some type which must tightly engage the face of the user circumambiently of the external respiratory organs, i.e. the mouth and the nose. When the user inhales this creates a partial vacuum in the mask, which means that the pressure in the mask is sub-atmospheric with reference to the ambient atmosphere. Due to the thus existing pressure gradient in direction inwardly of the mask, ambient air tends to leak into the interior of the mask and to reach the respiratory passages of the user. Depending upon the problems involved in the ambient atmosphere such leakage may be merely annoying if it is kept to a minimum or it may actually be dangerous or possibly even fatal.
It is, of course, already known that if super-atmospheric pressure is maintained in the mask at all times, i.e. not only during exhalation but also during inhalation, this will prevent the entry of ambient air at atmospheric pressure. However, it will also offer considerable additional resistance to the breathing function which makes breathing substantially more difficult than under ordinary circumstances, a factor which will be readily understood when it is kept in mind that normal breathing creates during the inhalation phase a slight underpressure (i.e. pressure below atmospheric pressure) in the outer respiratory passages and a slight overpressure (pressure above atmospheric pressure) during the exhalation phase.
A lung-controlled respiratory apparatus is known having a mask which engages the face of the user with a circumferentially standing seal and further having a breath-controlled dosing valve for the breathing air which is applied under pressure. The dosing valve has a control diaphragm the outer side of which is subject to ambient pressure and the inner side of which is subject to the pressure prevailing at interior of the breathing mask. The dosing valve is opened as a result of inhalation, for which purpose the inner side of the control diaphragm and the valve body are connected via tilt lever. The arms of the tilt lever are so dimensioned that the dosing valve is closed when the super-atmospheric pressure desired for the interior of the mask has been reached. The mask also has a vent valve which opens only when the super-atmospheric pressure desired in the interior of the mask is exceeded. This means that when the user exhales he must first overcome the interior pressure in the mask, i.e. he must exhale against the super-atmospheric pressure within the mask. His total exhalation pressure therefore is a product of the super-atmospheric pressure in the mask plus the additional pressure required to reach the operating pressure at which the vent valve will open.
For inhalation the breathing valve opens in response to the reduced super-atmospheric pressure which develops in the interior of the mask during the inhalation phase. During the entire inhalation phase there remains an over pressure in the interior of the mask which is sufficient to create a pressure gradient in direction outwardly towards the ambient atmosphere i.e. to prevent the leakage of ambient atmosphere into the mask of the device. This construction, disclosed in German Published Application OS No. 2,406,307, thus has the above-described desired advantage of preventing the infiltration of ambient air into the mask at all times. However, it does make breathing more difficult for the user, in the sense that the user must at least during exhalation overcome pressures greater than those encountered during normal breathing, so that the use of such a device leads to a certain amount of discomfort.